1. Field of the Invention
The present invention relates to a laser machining apparatus for performing machining such as drilling a circular hole in a planar object to be machined by means of a laser beam.
2. Related Background Art
Recently, a technology and an apparatus for machining, through processes such as continuously scanning or positioning and projecting a laser beam by using laser energy, heating and burning an object to be machined, sublimating or curing photo-curing resin into a desired shape as in a laser drilling machine, a laser marker or a photo forming machine have been expanded.
As one of such machining apparatus, there is a machining apparatus for converging a laser beam to a workpiece to form a hole therein as disclosed in Japanese Patent Application Laid-open No. 11-333575. In the conventional drilling machine, a galvanomirror for deflecting the beam and an XY table for holding the workpiece are moved to thereby position the beam and a high power beam is projected to perform drilling of a hole based on a size of a beam spot.
FIG. 1 is a perspective schematic view showing a condition where drilling is performed by means of a conventional laser machine. In FIG. 1, reference numeral 101 denotes an optical axis of a laser beam converged, and numeral 700 denotes a workpiece that is an object to be machined and disposed in the position of a beam spot 102 of the laser beam 101. Reference numeral 103 is a graph showing a distribution of optical energy of the laser beam in the beam spot 102. Thus, where the energy of the converged portion exceeds a constant threshold value 104, the temperature of the workpiece 700 is particularly elevated, the workpiece material is molten to be sublimated or chemically changed to gradually form a hole, and finally, a hole 701 passing through the workpiece 700 is formed.
However, in accordance with this method, it is difficult to obtain a hole having an appropriate form with high precision. This is because it is difficult to actually secure the ideal distribution of a true circular form in the energy distribution 103 for the threshold value 104 although the hole 701 is formed into a shape based on the energy distribution 103 of the beam spot 102. Also, since the laser beam is projected to the same position continuously, there is a fear in that the heat is locally accumulated. Accordingly, a blur of an inlet portion of the hole, the change in hole diameter in response to the position in the direction of the plate thickness, the degradation of the cylinder shape of the hole and the like may occur.
For this reason, the true circular degree of the hole formed in accordance with this system is only several to 10% of the diameter.
Accordingly, a method for forming a hole by removing a contour of the hole by rotating the beam spot having a smaller diameter than a diameter of the hole has been developed.
FIG. 2 is a perspective schematic view showing the condition where the hole is formed in accordance with this conventional method.
In FIG. 2, the same reference numerals as those in FIG. 1 are used to indicate the components with the same name and the explanation thereof will be omitted.
According to this method, since the light converged portion may be made small, the optical energy distribution 103 of the laser beam is abruptly changed in the beam spot 102 to obtain the energy distribution 103 with a sharp contrast. The small beam spot 102 is continuously moved to form a hole 202 in the workpiece 700 so that the machining may be performed under the condition where the precision of the inner surface of the machined hole 202 is the same as the track precision of the beam spot 102. Also, the machining is performed while sculpturing inch by inch many times so that the extra heat transmitted to the outside of the machined portion is likely to be radiated and diffused through the workpiece 700 and there is no fear that the blur of the inlet of the hole 701 and the change in hole diameter due to the heat would occur.
A biaxial galvanomirror system as shown in FIG. 3 has conventionally been adopted as a method for deflecting an optical axis of a laser beam for performing the machining of a hole having a high cylinder degree and a high true circular degree of such a hole. In FIG. 3, reference numeral 301 and 302 denote galvanomotors for driving reflector mirrors 303 and 304 mounted on respective galvanomotors 301 and 302 so as to perform the scanning of a laser beam 111 projected from a laser beam source 100 in two directions and converging laser beams 112 and 113 at desired positions of the workpiece 700 through an f-xcex8 lens (not shown). In this case, the operations of two galvanomotors 301 and 302 are caused to cooperate with each other and driven so that the beam spot depicts a circle on the workpiece 700.
In accordance with this system, since the portion to be mechanically driven is only the reflector mirrors 303 and 304, for example, it is possible to depict a circle at a higher speed than the system in which, as shown in a perspective view of the conventional case in FIG. 4, the laser beam 111, the reflector mirror 305 and a convergent lens 601 are fixed and the workpiece 700 is moved in a biaxial manner by the X-Y table 800 so that the circle may be depicted on the workpiece 700.
However, also in the conventional system using the galvanomirrors, under the recent circumstances that the required specification for the speed and the precision of the drilling has become severe, the following problems have been noticed and it is difficult to enhance the performance.
(1) As in the case where a hole is to be formed in a plate having a large thickness, it takes a long machining time when the beam spot is rotated many times to form the hole. Accordingly, even if a slight positional drift component exists in the positioning mechanism of the galvanomirrors, the true circular degree and the cylindrical degree of the hole become worse.
(2) The movable portion is only mirrors in the galvanomirror system. However, the mirrors have to be moved reciprocally. Also, in order to perform the cooperation operation of the two axises, the motion thereof must be performed with high precision, which cause the limitation to the speed.
In order to overcome the above-noted defects, an object of the present invention is to provide a laser machining apparatus that may perform the machining process at a high speed with high precision by performing rotation and deflection of the light beam and the optical axis with high precision and high reproducibility.